Objectives: Human leukocyte antigen incompatibility, particularly in broadly sensitized kidney transplant candidates with high calculated panel reactive antibody, poses a significant barrier to transplantation. Two strategies exist: (1) virtual crossmatch with a donor-specific antibody-free donor or (2) desensitization. We compared immunological risks and posttransplant complications between these 2 approaches.
Materials and Methods: We retrospectively screened 50 kidney transplant candidates with calculated panel reactive antibody ≥95%. Donor-specific antibody positivity was defined as mean fluorescence intensity >750. Of 25 participants (13 male; mean age 36.8 ± 14.3 years), 12 had calculated panel reactive antibody ≥95% and no donor-specific antibodies (group A), whereas 13 showed positivity for donor-specific antibodies and underwent desensitization (plasmapheresis, intravenous immunoglobulin, and rituximab with or without bortezomib; group B). All but 1 patient received living donor transplants. Sensitization included prior transplant (n = 22), transfusions (n = 23), and pregnancies (n = 7).
Results: Median follow-up was 18 months, with no significant difference in estimated glomerular filtration rate between groups at any time point (at day of discharge; at 1, 3, 6, 12, 18, and 24 months posttransplant, and at most recent follow-up). One graft loss occurred in group A due to vascular complications at 5 months. Sixteen biopsies were performed. Four episodes of acute antibody-mediated rejection were observed (1 in group A, 3 in group B; P = .⁷²⁸). Posttransplant infections occurred in 7 patients (28%), all in group B (P = .⁰⁰⁵), including BK virus (n = 5; P = .⁰³⁹) and parvovirus B19 (n = 2). Four patients in group A remained on immunosuppression versus none in group B (P = .⁰³⁹).
Conclusions: In highly sensitized kidney transplant recipients, both virtual crossmatch with donor-specific antibody-free donors and desensitization strategies resulted in comparable short-term graft function. However, desensitized patients showed significantly higher risk of posttransplant infections. Key words: Antibody-mediated rejection, Graft survival, Immunosuppression, Kidney transplantation, Posttransplant infection, Sensitization, Virtual crossmatch

Introduction
Kidney transplant remains the best therapeutic option for kidney replacement therapy in patients with end-stage renal disease and is associated with higher health-related quality of life, as well as a lower risk of mortality and cardiovascular events, compared with dialysis.^1,2 An increasing number of patients with a history of prior kidney transplant are returning to transplant wait lists worldwide due to chronic graft loss, and retransplant still has survival advantages in this population.³ Human leukocyte antigen (HLA) sensitization is an important barrier to kidney transplantation from both deceased and living donors. Contact with HLA antigens can lead to sensitization, which reduces the chance of transplant and worsens posttransplant outcomes. Prior transplant, history of pregnancy, and blood transfusions are the major sensitizing events, and prior transplant has a more powerful effect on sensitization compared with pregnancy and blood transfusions.^4,5 This higher immunological risk also increases the likelihood to develop de novo donor-specific antibodies (DSA), which are associated with a greater risk of antibody-mediated rejection (AMR) and adverse graft outcomes.⁶ Calculated panel reactive antibody (cPRA) quantifies the level of sensitization according to HLA frequencies in the population and is particularly useful for the decision process with regard to highly sensitized patients (eg, defined as cPRA ≥98% in some allocation systems).^7,8 In recent years, progress in immunogenetics, improved desensitization approaches, and allocation programs have expanded transplant options for highly sensitized patients.⁹ Desensitization is a therapeutic strategy to reduce DSA through plasmapheresis, intravenous immunoglobulin, and B-cell-targeted therapies. Although this strategy may be associated with specific complications, careful patient selection can potentially lead to improved graft survival and patient survival.¹⁰ Alternatively, strategies such as acceptable mismatch allocation or kidney paired donation increase access to compatible organs by finding donors against whom the recipient has no clinically relevant antibodies, thereby avoiding the need for antibody reduction.⁷ In the present study, we reviewed patient records at an Iranian transplant center affiliated with Middle East Society for Organ Transplantation with an aim to evaluate and compare graft function, AMR incidence, infection rates, and short-term survival in 2 groups of highly sensitized kidney recipients undergoing either (1) virtual crossmatch (VXM) transplant from a DSA-free donor or (2) desensitization-based transplant.

Materials and Methods

Study design and setting
This retrospective single-center cohort study was conducted at Shahid Labafinejad Hospital, Tehran, Iran, which is a tertiary referral center for kidney transplant affiliated with Shahid Beheshti University of Medical Sciences. The study period was January 2023 through December 2025. All procedures conformed to the ethical standards of the institutional review board (IR.SBMU.REC.¹⁴⁰³.156) and adhered to the Declaration of Helsinki and the Declaration of Istanbul on Organ Trafficking and Transplant Tourism. Initially, 50 kidney transplant recipients with a cPRA ≥95% were screened, of whom 25 highly sensitized recipients (12 female, 13 male) met the inclusion criteria and were enrolled in the study.

Inclusion and exclusion criteria
Inclusion criteria consisted of adult kidney transplant recipients aged ≥18 years with a cPRA ≥95% who had complete pretransplant and posttransplant immunology data available and underwent 1 of 2 transplant strategies, that is, either VXM DSA-free transplant (VXM group) or desensitization prior to transplant (desensitized group). We excluded patients who underwent multiorgan transplant or demonstrated ABO incompatibility and patients with incomplete follow-up data.

Study groups
The highly sensitized kidney transplant recipients were divided into the following 2 groups based on the transplant strategy: the VXM group (n = 12) and the desensitized group (n = 13). Patients in the VXM group had no detectable DSA, defined as a mean fluorescence intensity <500 on Luminex single-antigen bead assays, and underwent kidney transplant without the need for desensitization. Patients in the desensitization group had positive test results for DSA, defined as mean fluorescence intensity >750, and underwent a desensitization protocol prior to transplant. The desensitization protocol included 3 to 5 sessions of plasmapheresis, followed by intravenous immunoglobulin at a dose of 100 mg/kg after each session, and a single dose of rituximab (375 mg/m²) at the end of the treatment course. Bortezomib was additionally used in patients with refractory DSA, with the aim to reduce antibody levels below the predefined positivity threshold.

Patient follow-up and outcomes
All patients received anti-thymocyte globulin induction and a standard triple immunosuppression regimen consisting of tacrolimus, mycophenolate mofetil, and prednisolone following kidney transplant. They were followed for up to 24 months after transplant, with a median follow-up of 18 months. Clinical and laboratory assessments were performed at time of discharge and at 1, 3, 6, 12, 18, and 24 months after transplant. Renal allograft function was evaluated according to the estimated glomerular filtration rate (eGFR) as calculated with the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation for eGFR. Assessment of DSA followed established guidelines. In the desensitized group, DSA was assessed on posttransplant day 4 and subsequently after transplant at 2 weeks, 4 weeks, 8 weeks, 6 months, and 1 year. In the VXM group, DSA assessment occurred at 4 weeks, 6 months, and 1 year after transplant. All kidney biopsies performed for any indication during the follow-up period were recorded, and episodes of biopsy-proven AMR were identified and defined according to the Banff 2019 criteria. In addition, posttransplant infectious complications, including viral, bacterial, and fungal infections, were documented.

Data collection and analyses
Clinical and laboratory data were retrieved from the Iranian Kidney Transplant Registry. Infectious episodes were confirmed by laboratory and histopathology evidence.

Statistical analyses
We expressed continuous variables as mean ± SD and categorical variables as frequency (with percentage). Comparisons between groups were performed using the Student t test or the Mann-Whitney U test for continuous variables, as appropriate, and the Fisher exact test for categorical variables. P < .⁰⁵ was considered statistically significant. We used SPSS software (version 26.0; IBM) for all statistical analyses.

Results

Baseline characteristics
The 2 groups were demographically comparable regarding age, sex, prior transplants, and transfusion history (Table 1). Among the 25 highly sensitized kidney transplant recipients, their ages ranged from 19 to 70 years (mean 36.8 years), and 13 patients (52%) were male. Based on the transplant strategy, 12 patients underwent VXM DSA-free transplant, and 13 patients showed positive results for DSA and underwent desensitization before transplant. The mean age of patients in the VXM group was 42.8 ± 8.5 years versus 31.4 ± 9.2 years in the desensitized group; this difference was at the borderline of statistical significance (P = .⁰⁵⁰⁵). Regarding transplant number, 19 patients (76%) underwent a second kidney transplant, 4 patients (16%) received their first transplant, and 2 patients (8%) underwent a third transplant. One patient in the VXM group had graft loss due to vascular complications at 5 months. In the desensitized group, 12 patients received a living donor kidney transplant, and only 1 was a recipient of a deceased donor transplant. A history of previous kidney transplant was present in 22 patients (88%), and 23 patients (92%) had a history of blood transfusion. Seven of 12 female patients (58%) had a history of pregnancy, and 3 of them (25%) reported a history of aborted pregnancy. Of the female recipients without a history of pregnancy, 4 patients had previous transplant and transfusion exposure, and 1 patient had a history of prior transplant alone. History of prior kidney transplant was present in 11 patients (91.7%) in the VXM group and 11 patients (84.6%) in the desensitized group, without a significant difference. Similarly, a history of blood transfusion was reported in 11 patients (91.7%) in the VXM group and 12 patients (92.3%) in the desensitized group (P = .⁷³).

Biopsy findings and rejection episodes
Sixteen kidney allograft biopsies (64%) were performed during the follow-up period. Biopsies were indicated in cases of a rise in serum creatinine greater than 25% above baseline, new-onset proteinuria, or a significant increase in DSA levels. We identified 4 patients (16%) with acute AMR and 1 case of chronic active AMR. In addition, 2 biopsies demonstrated T-cell-mediated rejection. The incidence of AMR was higher in the desensitized group (23.1%) versus the VXM group (8.3%); however, this difference was not significant (P > .⁰⁵) (Table 2). The median follow-up duration was 18 months. During this follow-up period, renal allograft function was assessed according to the CKD-EPI equation for eGFR. Overall, the results demonstrated no significant differences in mean eGFR between the 2 groups at any of the evaluated time points (P > .⁰⁵). Seven patients (28%) developed posttransplant infections (including BK virus and parvovirus B19 infection), all of whom belonged to the desensitized group. BK virus infection occurred in 5 patients (20%), exclusively in the desensitized group, and 2 patients developed parvovirus B19 during follow-up. Graft survival was analyzed using the Kaplan-Meier method. Comparison of graft survival curves between the 2 groups demonstrated no significant difference in graft survival between the 2 groups (log-rank test, P = .⁹²⁴) (Figure 1). The 2-year graft survival in the VXM group was 100% and 92.3% in the desensitization group (P = .³⁸⁶) (Figure 2).

Discussion
In our study cohort, patients in the desensitized group were younger than the patients in the VXM group, with a borderline significant difference in mean age. This age difference may reflect a degree of clinical selection, as younger patients are often considered better candidates for intensified immunological interventions due to lower frailty and greater physiological reserve. In the present study, graft survival did not differ significantly between the VXM group and the desensitized group during the follow-up period. Our findings suggest that, at least in the short-term to mid-term follow-up, graft survival is comparable between the 2 strategies when appropriate immunological management is applied. Similar findings have been reported in prior studies. Noble and colleagues¹¹ reported acceptable 1-year graft survival rates in desensitized recipients, suggesting that desensitization can allow successful transplant despite immunological risk. However, they also noted that long-term graft survival is lower in desensitized patients versus DSA-free recipients. Similarly, Sharma and colleagues¹² have reported that graft survival in desensitized patients was comparable to standard recipients when DSA were adequately reduced, despite higher rejection rates. In our study, the incidence of AMR was higher in the desensitized group (23.1%) versus the VXM group (8.3%). Although this difference was not statistically significant, the observed trend suggests a greater immunological risk among patients undergoing desensitization prior to transplant. Peak pretransplant DSA levels have been shown to better predict AMR than concurrent antibody levels, which may partly explain the higher rejection rate observed in our desensitized patients despite antibody reduction therapy.¹³ Noble and colleagues¹¹ have emphasized that desensitized crossmatch-positive recipients experience higher rates of AMR versus DSA-free transplant recipients, despite improved access to transplantation. Furthermore, Lee and colleagues¹⁴ have identified AMR as a major determinant of inferior graft outcomes and showed that desensitization does not completely eliminate the risk of antibody-mediated injury. Taken together, these studies support the result observed in our study, that is, desensitized patients exhibited a higher rate of AMR versus DSA-free recipients. Importantly, the absence of statistical significance in our study was likely attributable to the relatively small sample size (n = 25) and the limited number of rejection events. Larger cohorts or multicenter studies would be required to determine whether the observed numerical difference translates into a statistically significant and clinically meaningful disparity. In the present study, all posttransplant infectious complications occurred in the desensitized group, and BK virus infection was observed exclusively in these patients. This finding suggests that desensitization therapy may be associated with an increased risk of infectious complications, particularly viral infections such as BK virus reactivation. Because BK virus infection is closely linked to the degree of immunosuppression,¹⁵ the higher rate of BK nephropathy in our desensitized cohort may be explained by the more intensive immunosuppression therapy administered in this group.

Conclusions
In this cohort of highly sensitized kidney transplant recipients, short-term graft survival did not differ significantly between patients undergoing desensitization versus transplant recipients who underwent a DSA-free virtual crossmatch strategy. Although the incidence of AMR was numerically higher in the desensitized group, this difference was not significant. However, infectious complications, including BK virus nephropathy, occurred significantly more frequently among desensitized recipients. These findings suggest that a high cPRA alone may not be an independent predictor of short-term graft survival. When a compatible donor is available, DSA-free transplant may be preferable to desensitization in order to minimize immunological and infectious complications. Larger studies with longer follow-up are warranted to further clarify long-term outcomes between these 2 strategies.